This invention relates to a method of and apparatus for qualitative analysis such as fluorescent X-ray spectrometry and emission spectral analysis wherein a sample is excited and the signal light emitted therefrom is spectroscopically analyzed to identify the elements contained in the sample. More particularly, this invention relates to the technology of carrying out accurate qualitative analyses by eliminating the effects of chemical shifts.
For carrying out a qualitative analysis of a sample with a fluorescent X-ray spectrometer, for example, it has been known to preliminarily store the wavelengths of various elements in a memory device as a database, to find the wavelength corresponding to the detection angle 2xcex8 of each of the peaks of the spectrum obtained from the fluorescent X-ray from the sample, to compare them with the database, and to identify the elements which show values close to those in the database. The target elements to be analyzed in a sample (such as Al, Si, O, S, Mg and B), however, do not always exist in the elemental form but may frequently be in the form of a compound such as an oxide or a nitride. When an element is in the form of a compound, what is known as xe2x80x9cthe chemical shiftxe2x80x9d is observed, that is, the peak for that element appears at a shifted wavelength compared to when the element is in the elemental form. FIG. 3 shows how the profile of elemental boron shown by the solid line changes to the one shown by the broken line in the case of B2O3 where boron appears in a compound with oxygen, the peak shifting by xcex942xcex8.
The chemical shift is generally more pronounced for elements with small atomic numbers, or light elements. It is probably because a light element has only a small number of electrons and its energy state is more likely to be influenced by the conditions of its K-shell electrons due to its chemical bonding. In a situation where the chemical shift xcex942xcex8 is greater than the error in the optical system for measuring the fluorescent X-ray, the measured peak position will not agree with the peak position in the database, and hence the element may fail to be identified, or an element corresponding to an incorrect spectral line may be identified.
It is therefore an object of this invention to eliminate such problems of incorrectly identifying elements in a qualitative analysis of a sample due to the chemical shift of the elements such that qualitative analyses can be carried out with improved reliability.
An apparatus for qualitative analysis embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a data memory for storing measured spectral line data obtained by exciting a sample and spectroscopically analyzing signal light emitted from the sample, a database memory which stores reference spectral line data of various elements in different compound forms, and a data analyzer for determining whether the measured spectral line data include spectral lines of specified compound-forming elements such as oxygen and nitrogen and, if the measured spectral line data include spectral lines of any of these compound-forming elements, comparing the reference spectral line data with the measured spectral line data to thereby identify elements in the sample.